In the fifth version of this manual, published in May, individuals with autism spectrum disorder are those who meet the following criteria - persistent deficits in communication, restrictive and repetitive behavioral patterns, symptoms that are present in early childhood, and symptoms that limit and impair everyday functioning.

If the criteria sound vague, that's because they are.

The reality is that individuals with autism can exhibit the listed behaviors with varying degrees of severity. For Christian Goff, a 12-year-old Spring Grove boy who is on the lower end of the spectrum, that means an inability to carry out a full conversation. For others, like Dakota Reiner of Hanover, who has asperger's syndrome and is therefore on the higher end of the spectrum, it means a difficulty in sustaining relationships or picking up on more nuanced language, such as sarcasm.

"With Dakota, he doesn't understand sustaining relationships," said Dakota's father, Paul Reiner, who belongs to a local autism fundraising organization. He explained that sometimes when friends come over to play with Dakota, he just wanders off to do his own thing whenever he gets bored.

"He has no perception of how people look at him," Paul added.

Despite the social difficulties that autism has brought him, Dakota's intellect has not suffered, Paul said. He can take apart a Nerf gun and put it back together so that it shoots farther. He learns at the same pace as the average student.

At first glance, the differences between Christian and Dakota seem vast. Christian cannot read or write, while Dakota excels at school, but as Kittelberger explained, this is where the "spectrum" in autism spectrum disorder comes into play.

"You can have a communication disorder where you never learn to talk, or you can have a communication disorder where you can talk, but have a hard time understanding abstract words," Kittelberger said. "They involve the same brain function, with varying degrees of impairment."

A growing scientific consensus has found that this impairment originates with gene mutations, known as de novo, in the early stages of prenatal development.

"The dogma has always been that mutations are very rare," Kittelberger said. "We are starting to realize that's not true. You probably have 50 to 100 de novo mutations that neither of your parents have."

Of these de novo mutations, must of them have no effect on people, Kittelberger said, but some are associated with mental health. Genes involved with brain development are especially susceptible to these mutations, he added, which could explain why mental disorders such as autism and schizophrenia exist.

This could also help to explain Christian's diagnosis. Neither of his parents are autistic, so typical genetic reasonings don't necessarily apply. But, if autism really is the result of deviations in the genes of the parents, then that could help to explain why Christian has autism when it does not appear to run in the family.

This however is not necessarily comforting for parents like Christian's mother, Kim Goff, who are then left to wonder, why did these gene mutations occur? Or was it even gene mutations at all? Scientists are still grappling with these issues themselves, investigating any environmental factors that could possibly be contributing to these mutations.

After all, if autism rates are actually increasing, then there must be some external factor driving the increase in gene mutations.

A study released last summer found that one of those factors could be age. Researchers discovered that a 40-year-old father is likely to produce a child with more than twice as many paternal mutations as a 20-year-old father.

"This may explain the increase in autism," Kittelberger said, "since people are having kids later."

The connection however, is far from direct. The risk of a man 40 or older having a child with autism is still only 2 percent. And Kim's husband, William, was still relatively young when they had Christian.

So this is the situation parents are faced with - de novo mutations only account for a fraction of autism cases, and age can have an impact, but not always, and a myriad of other studies out there have only managed to partially tie other factors to autism.

In the pursuit of scientific discovery, these uncertainties are to be expected as the compendium of knowledge grows and grows, but for parents, the haziness only leads to more frustration and confusion.

In this climate, it is no wonder that vaccines given for common diseases have emerged as the most suspected environmental factor, at least among lay people. This lack of definitive autism testing, paired with the timing of the disorder's emergence in young children has resulted in an only natural association of autism and vaccines in the minds of many.

Parents don't often realize that their child has a communication disorder until they are old enough to talk, Kittelberger said, which just so happens to coincide with the time when most booster shots are given. For parents, this can mean playing with their seemingly healthy child one day and then dealing with the realities of their diagnosis the next. Many parents say it's as if a light went off in their child, as communication barriers suddenly become more and more severe, but according to Kittelberger, those deficits had probably been there all along.

"I don't know of anything environmental affecting kids after they are born," Kittelberger said. "Once you're born, the brain has already mostly developed. So much has already happened. The basic structure of the brain has been laid out."

The argument for a link between vaccines and autism is based around a 1998 study, which has since been thoroughly discredited. That study led vaccine-skeptics to claim that the amount of antigens in vaccines overwhelmed babies' immune systems, making them more susceptible to the disorder.

But mountains of scientific studies have since discredited that 1998 study. In a new study released in March by the Centers for Disease Control and Prevention, researchers compared the vaccine histories of 250 autistic children with those of 750 typical kids, comparing the number of antigens that each child received from vaccines. Not only did they find no correlation, but scientists also discovered that the number of antigens in vaccines has actually gone down since the late 1990s.

"It has been tested up, down and sideways," Kittelberger said, "and there is no connection between vaccines and autism."